IC chips rapidly decrease in the yield rate at the time of manufacture as they increase in size. For example, in a case where the yield rate, which is the ratio of the total number of usable IC chips to the total number of manufactured IC chips, is 50%, when the area of the IC chips is doubled, the yield rate is ½ squared, that is, ¼. When the area of the IC chips is quadrupled, the yield rate is ½ to the fourth power, that is, 1/16. Therefore, when one chip costs 100,000 yen, a chip having a quadruple area costs as high as 1,600,000 yen.
In the case of normal IC chips, a chip having substantially the same function as a quadruple-area chip can be manufactured by simply arranging four separately manufactured usable chips. However, to manufacture an image sensor having a quadruple area, it is necessary to join the image capturing areas so that no line appears on the reproduced images, which requires a high technology.
A technology for manufacturing a large-area image sensor by arranging image sensors has already been used, and such an image sensor is called a buttable image sensor. For example, in scientific field such as astronomy in which large-area image sensors are required, allowing the demarcation lines between blocks to appear on the reproduced images, very-large-area image sensors are manufactured by the buttable image sensor technology.
On the other hand, some image sensors are of a parallel read-out type intended for high-speed read-out and the like. In this type, the image capturing area is divided into a plurality of blocks, an image information read-out line is provided for each block, and the image information is read out to the outside of the image sensor in parallel.
For example, by dividing the image capturing area of a chip into four blocks along the longitudinal and lateral demarcation lines so that each block functions independently, even when one of these blocks has a significant defect that makes image capturing substantially impossible, image capturing can be performed by the other blocks. Therefore, if at least one of the four blocks is normal, by performing image capturing with only the image capturing possible block, the chip can be used as an image sensor with a small number of pixels. Moreover, by cutting the chip so as to include the image capturing possible block, the normal block can be used without waste.
Even though the cut chip is different in size, the external control circuit for controlling the image sensor is the same. By making it possible to replace such image sensors with different sizes and similar control manners, the range of usability of one image capturing apparatus can be increased. Such an image capturing apparatus with a replaceable image sensor is disclosed in Japanese Laid-Open Patent Application No. H04-68873 of the present inventor.